Electric circuit comprising electric discharge device



y 1952 J. M l. FERGUSON ETAL 2,597,980

ELECTRIC CIRCUIT COMPRISING ELECTRIC DIESCHARGE DEVICE Filed Dec. 19.1949 2 SHEETS-SHEET 1 INVENTORS JOHN ll. FERGUSON CLIFFORD BROWN AT TORNEYS May 27, 1952 J. M I. FERGUSON ET AL ELECTRIC CIRCUIT COMPRISINGELECTRIC DISCHARGE DEVICE Filed Dec. 19. 1949 2 Sl-EETS-SHEET 2 It /\lINVENTORS: JOHN M. FERGUSON CLIFFORD BROWN.

FIG. 2.

BY 6% 76M ATTORNEYS Patented May 27, 1952 ELECTRIC CIRCUIT COMPRISINGELECTRIC DISCHARGE DEVICE John McIntyre Ferguson and Clifl'ord Erown,

Stafford, England, assignors to: The English Electric Company Limited,London, England, a

British company Application December 19, 1949, Serial No: 1 38,884

In Great Britain December 31, 1948 This invention relates to electricalpulse generating circuits.

An object of the invention is to provide a pulse generating circuitsuitable to serve as a radar modulator and to handle pulse powers up tothe order of 10 megawatts and more.

In carrying the invention into efiect, a pulseiorming network is chargedthrough a step-up transformer from a source of alternating currenthaving frequency equal to that of the pulserepetition required, and isdischarged by a pulse of very heavy current through a load and through adischarge tube of the mercury pool type. This discharge is immediatelypreceded by another heavy current discharge through the tube.

Fig. l of the accompanying drawing illustrates diagrammatically a pulsegenerating circuit which embodies the invention in preferred form. Thiscircuit is employed as pulse modulator in a radar transmitter. Fig. 2illustrates the wave forms at various points in the circuit of Fig. 1.

The network is a pulse-forming network which is alternately charged,relatively slowly, from an alternating current generator l2 anddischarged, very rapidly, through a load [3.

The frequency of the alternating current generated by generator [2 isequal to the repetition frequency required for the pulses, which may beabout 500 cycles per second. At this frequency, network It! presentsimpedance which is substantially a capacitance. It is charged fromgenerator I2, during part of a cycle thereof, through a step-uptransformer II and a choke 26, and it reaches a potential of about 20kilovolts.

The discharge path for the network It comprises in series the load [3,represented as a resistance, and the arc path from anode M to cathode |5of a mercury pool discharge device. The discharge ofthe network l0 takesthe form of a square-wave pulse of very heavy current, say about 500amps, subsisting for about one or two microseconds.

The mercury pool discharge device is provided with an igniter l6supplied with current from a direct current source 21 of about 100volts, this current being under control of a push-button l1 and limitedby series resistor 28.

The direct current source 2'! also supplies current through choke 29 andresistor 31 to an excitation anode l8. This current is limited byresistor 31 to about 5 amps, and maintains a steady excitation are fromanode 8 to cathode j 3 Claims. (01. 250-27) 15 after the igniter hasbeen operated. byv pushbutton ll.

In order to avoid the danger that the excitation are may be quenchedwhen network I0 is discharged, a further anode I9 is arranged todischarge a condenser 20 during the period covering the instant whendischarge of network 10 is to occur.

Condenser 20 is charged substantially linearly ;from a direct currentsource 2| through a large inductance 22. Once in every cycle ofalternating source 12, condenser 20 is discharged by a heavy currentflowing through inductance 23 and the path between anode l9 and cathodeI5. The

discharge is initiated, about 50 microseconds in advance of the instantfor discharge of network I 0, by application of a firing pulse tocontrol grid 24 which covers anode l9. Inductance 23 and condenser 20are so proportioned that the discharge current will have the form of ahalf sine wave of duration about microseconds and peak value about amps.About the instant when this current reaches its peak, a firing pulse isapplied to control grid 25 which covers anode l4, and the very rapiddischarge of capacitance to through load 13 then occurs.

The firing pulses for the control grid 24 are derived from a smallalternating current generator 30 which is coupled to generator I2 andproduces alternating current of the same frequency. The output ofgenerator 30 is applied through a phase shifter 3| to a pulse generator32, from which firing pulses are applied over bias source 33 to controlgrid 24. Phase shifter 3| can be adjusted so that these firing pulsesoccur when network I0 is charged and ready for discharge.

The firing pulses for the control grid 25 are applied from a pulsegenerator 34 over bias source 35. Pulse generator 34 is controlled frompulse generator 32 through time delay network 38,

which can be adjusted to give the desired interval between the firingpulses on control grids 24 and 25.

In Fig. 2-

Wave form Vl2 represents the 500 cycles per second sine wave voltagegenerated by the generator l2 of Fig. 1.

Wave form V24 represents the voltage of control grid 24 relative tocathode [5.

Wave form V20 represents the voltage across condenser 20.

Wave form Ii 9 represents the intermittent half sine wave dischargecurrents from anode Is. The time scale is exaggerated relative to thatof wave forms V12, V24, V20, because the duration OFFICE of each ofthese discharges from anode I9 is only about 100 microseconds.

Wave form V25 represents the voltage of control grid 25 relative tocathode l5.

Wave form-y represents the voltage between anode H and cathode l5.

Wave form IIS represents the current pulses through load l3; and as eachof these has .a duration of only about two microseconds, the time scaleis'exaggerated even more than that of wave form I19.

In the method of operating the apparatus which has been described,the'discharge between anode l4 and cathode I5 is timed to occur when"that between anode l9 and cathode I5 is near its peak. Alternatively,however, the discharge between anode l4 and cathode 15 may be timed tooccur at any time up to 100 microseconds later than this.

What we claim as our invention and desire to secure by Letters Patentis:

1. An electrical pulse generating circuit com prisinganelectric-discharge tube having a mercury poolcathode a first anodeprovided with a first controligrid, and a. second anodeprovided with asecond controlgrid; aload, .a first capacitance, a path for dischargingsaid first capaci" tance through said load and through the arc pathbetweerrsaid first anode and said cathode by a'veryheavy currentsubsisting fora period of the order of microseconds upon the appiiea=tion ofafiring pulse tosaidfirst control grid;

an" alternating current source-and a step-up transformerarrangedtocharge said first capacitance; a second capacitanceconnected in seriesforms a substantially sinusoidal half-wave subsisting for a period ofthe order of hundreds of microseconds, and means to apply a firing pulseto-said first control grid at a time within a period of loo-microsecondscommencing during said heavy current discharge.

2. A circuit according to claim 1, wherein the electricdischarge tube isprovided with means to maintain a continuous excitation arc therein.

'3. A circuit according to claim 2, wherein the electric dischargedevice is provided with an igniter for initiating-the excitation are.

JOHN MCINTYRE FERGUSON. CLIFFORD BROWN.

REFERENCES. CITED The following references are of record in" the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,242,948 Gulii ksen d- May 201941 2,288,554- Smith June 30; 1942 2,458,574 Dow Jan. 11, 19492,498,257

Douma Feb. 21, 1950

